For resource saving, energy saving, and environmental protection, the society increasingly demands reduction in carbon dioxide gas emission. In order to also reduce the carbon dioxide gas emission of cars, various measures have been considered, including for example car weight reduction and the use of electric energy.
A common challenge in the automotive field is the need to enhance fuel economy by improving the rolling resistance of tires, and there are also increasing demands for enhanced safety during driving and enhanced durability. Since these properties greatly depend on the performance of tires, tires for cars are increasingly required to have improved fuel economy, wet grip performance, handling stability, and durability (e.g. abrasion resistance). The performance of tires depends on various factors, including the structure and materials of tires, and greatly depends particularly on the performance of the rubber composition used in the tread part which comes into contact with the road surface. For this reason, a wide range of studies have been undertaken to technically improve rubber compositions for tires such as for treads and these techniques have been put into practical use.
It is known to improve the fuel economy of a rubber composition by reducing the amount of filler or by using a modified polymer (see, for example, Patent Literature 1). However, when the amount of filler is reduced or when filler is highly dispersed, rubber stiffness tends to be reduced, which leads to the problem of decrease in kinematic performance (e.g. handling stability) of tires.